Welding transformer with colled core



g- 1964 D. F. DUNNABECK ETAL 3,

' WELDING TRANSFORMER WITH CQOLED CORE Filed July 5, 1960 INVENTOR.

P ARTHUR w. BULL F y DONALD F. DUNNABECK fi MAM,

ATTORNEY United States Patent WELDING TRANSFORMER WITH COOLED CORE Donald F. Dunnabecit, 871 Wood Lane, Bloomfield Hills,

Mich, and Arthur W. Bull, Windsor, Ontario, Canada;

said Bull assignor to Welder: Division of Metal Craft Co., Detroit, Mich, a corporation of Michigan Filed July 5, 196%, Ser. No. 40,635 2 Claims. (Cl. 33655) This invention relates to a stepdown transformer of the type used in connection with resistance welding apparatus and, more particularly, to such a transformer as may be used in connection with welding control systems which supply power which includes high frequency components.

Resistance welding units commonly employ control systems adapted to supply line power to the primary of a stepdown transformer for controlled periods of time. This power is often of a commercial frequency such as 60 cycles per second. Such transformers may have secondaries consisting of a plurality of paralleled copper tubes which encircle the core. Cooling fluid is circulated through these tubes to dissipate the heat generated by the high currents that flow through the secondaries.

The primary of such transformers are necessarily formed with a large number of turns of finer wire which are, therefore, not adaptable to be cooled as are the secondary turns. Similarly, the core of the transformer must necessarily be formed of a stack of laminations to reduce eddy currents and is, therefore, not adaptable to cooling by the circulation of the fluid through it.

It has been recently discovered that advantageous results may be obtained by applying power to the primary of welding transformers in the form of a sharp pulse rather than a sinusoidal wave. The advantages attributable to such control systems include the application of current to the workpiece at a high rate so that the heating effect is not greatly diminished by heat lost to the atmosphere.

While the pulses provided from such control systems occur at frequencies no greater than and often less than commercial line frequency, the sharp nature of the pulses reveals a group of high-frequency components upon Fourier analysis. Therefore, these pulses provide the effects of such high frequency currents including the increase in eddy currents in the transformer core.

Because of the difficulty associated with directly cooling the transformer primary or the laminated core, as noted above, the present invention contemplates a weld ing transformer for use with sharp input wave forms which employs a solid, central non-magnetic section disposed within the core which may be water cooled to dissipate the heating effect of the high frequency components of the sharp wave forms.

It is, therefore, an object of the present invention to provide a stepdown transformer which may be used as the output of a resistance welder control unit of the type which provides sharp wave forms having both high and low frequency components.

Another object is to provide such a transformer which minimizes eddy currents and efficiently dissipates the heat generated in the core.

Other objects, advantages and applications of the present invention will be made apparent by the following detailed description of a preferred embodiment of the invention. The description makes reference to the accompanying drawings in which:

FIGURE 1 represents a side view of a transformer embodying the present invention, partially cut away to better illustrate the structure of its core;

FIGURE 2 represents a cross-section of the transformer taken along lines 22 of FIGURE 1; and

3,144,627 Patented Aug. 11, 1964 ice FIGURE 3 is a side view of a pair of solid core elements, one of which is shown in cross-section.

The core of the transformer is formed of a first group of laminations, generally indicated at 10, a second group of laminations, generally indicated at 12, and a solid metallic central section, generally indicated at 14. The laminations are the normal type used in such transformers, being formed of thin sheet silicon alloy steel. As may be seen in FIGURE 2-, the cross-section of the laminations 16 is formed of two lamination pieces, each generally E-shaped with cutbacks on their center legs. When placed together, a pair of laminations form a pair of rectangular areas enclosed on four sides.

The laminations are formed into the two stacks 10 and 12 which sandwich a central solid cross-section 14 comprised of two identical E-shaped sections 18.

The solid sections 18 have center legs which are slightly longer than their end legs so that when two sections are assembled with the faces of their central legs abutting one another, an air gap 20 is formed between the adjacent surfaces of the end sections. The abutting faces of the two center legs of the core section 18 are joined by a thin gasket or insulating partition 22. The air gaps Z0, and the gasket 22, prevent the solid core section 18 from acting as a secondary and conducting induced currents.

The solid core sections 18 are joined by a pair of bolts 24 which pass through their center legs.

Each section has a water passage 25 which passes centrally through its side to the center where it makes a right angle turn and passes out through the middle of the center leg. The sections are enjoined in an inverted manner so that the center passages are joined through a hole in the gasket 22 and the cooling fluid goes up one side of the center core section 18 and down the other side. Water fittings 28 at the termination of each passage allow the cooling fluid to be removed and introduced from the passages.

The solid core members 18 are formed of aluminum or another similar non-magnetic metal. The sandwich composed of the lamination sections 10 and 12 and the central core section 14 are held together by a pair of end bells 30 joined by elongated bolt sets 32 which draw them together.

The primary of the transformer is composed of a plurality of turns of relatively fine wire 34 which is wound about the central leg of the laminations and core member 18, and which is tape wound as at 36, for insulation purposes. The secondary of the transformer comprises a group of copper tubes 38 formed in a horseshoe shape so as to surround the primary on three sides. At their terminations, the copper tubes 38 are shunted together by a pair of manifolds 40 which receive cooling fluid through side passages 42 and distribute it through the secondary tubes 38.

The cooling water may be circulated through the core passages 25 and the secondary tubes 38 in series, or separate connections may be made to each of them, depending upon the temperature and pressure of the water system available and the rate of utilization of the transformer.

A control system which the present transformer might be used as the output of is illustrated in patent application No. 833,766, new Patent No. 3,074,009, for a Pulse Power Welding System, filed by Donald F. Dunnabeck and Arthur W. Bull. That type control system provides spikes of power to the transformer intermittently. These spikes are sharp wave forms which include a wide variety of frequency components.

Having thus described our invention, we claim:

1. A core for a welding stepdown transformer adapted to receive non-sinusoidal power pulses in its primary, comprising: a pair of identical stacks of thin magnetic laminations enclosing tWo space areas so as to form two separate magnetic paths having a single common leg and two non-common legs; a solid core part formed of tWo identical pieces of nonmagnetic material shaped similarly to said lamination stacks out differing therefrom in having an air gap in each of said non-common legs and an insulating partition in said common leg; cooling passages in each of said solid core part halves connecting at said partition in said common leg; and fastener means for disposing said lamination stacks on the opposite sides of said solid core part and in an abutting relationship thereto.

2. A core for a stepdown Welding output transformer, adapted to receive non-sinusoidal power pulses in its primary, comprising: a pair of identical magnetic lamination stacks formed generally as a figure 8; a solid nonmagnetic central core section comprised of two identical halves, each E-shaped with their central legs slightly longer than their two outer legs, said core section being joined with their center legs separated by a thin gasket so as to form a configuration having relatively large air gaps in the outer legs and a relatively thin insulation gap in the center leg; a means for joining said lamination stacks and said core section in a sandwich relation With the lamination stacks in the outer sides.

References Cited in the file of this patent UNITED STATES PATENTS 2,141,573 Vogt Dec. 27, 1938 2,261,323 Zierdt Nov. 4, 1941 2,547,045 Sahol Apr. 3, 1951 2,547,065 Wadhams Apr. 3, 1951 2,577,825 Strickland Dec. 11, 1951 

1. A CORE FOR A WELDING STEPDOWN TRANSFORMER ADAPTED TO RECEIVE NON-SINUSOIDAL POWER PULSES IN ITS PRIMARY, COMPRISING: A PAIR OF IDENTICAL STACKS OF THIN MAGNETIC LAMINATIONS ENCLOSING TWO SPACE AREAS SO AS TO FORM TWO SEPARATE MAGNETIC PATHS HAVING A SINGLE COMMON LEG AND TWO NON-COMMON LEGS; A SOLID CORE PART FORMED OF TWO IDENTICAL PIECES OF NON-MAGNETIC MATERIAL SHAPED SIMILARLY TO SAID LAMINATION STACKS BUT DIFFERING THEREFROM IN HAVING AN AIR GAP IN EACH OF SAID NON-COMMON LEGS AND AN INSULATING PARTITION IN SAID COMMON LEG; COOLING PASSAGES IN EACH OF SAID SOLID CORE PART HALVES CONNECTING AT SAID PARTITION IN SAID COMMON LEG; AND FASTENER MEANS FOR DISPOSING SAID LAMINATION STACKS ON THE OPPOSITE SIDES OF SAID SOLID CORE PART AND IN AN ABUTTING RELATIONSHIP THERETO. 